In the operation of a resonant fiber optic gyroscope (RFOG), it is desirable to lock the frequencies of the laser light sources to the resonance frequencies of the fiber optic ring resonator using high bandwidth electronic servos. Currently, that can be achieved by using a reflection port detector signal from the resonator because signals from the reflection port have a high speed response to frequency changes in the light from the laser light sources. The output signal from a reflection port includes light coming directly from the laser and also includes light coming from the output of the resonator coil. In contrast, the output signal from a transmission port only includes light which has circulated through the resonator coil. For this reason, light from the reflection port has a much faster response to changes in optical frequency compared to light from the transmission port. Further, because the output of the transmission port only includes light that has propagated through the resonator coil, the light from the transmission port will not include light having spatial or polarization mode mismatch or cross coupling, which create biases that may lead to rotation rate measurement errors. In contrast, the output of the reflection port in RFOGs today does include a component of light having a polarization that does not match the Eigen-state of polarization (ESOP) in the resonator, causing resonance lineshape asymmetry, and leading to bias errors that make it unsuitable for obtaining rotation rate measurements made at the reflection port.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for systems and methods to reduce or eliminate resonance asymmetry at the reflection port of an RFOG.